1. Field of Invention
The present invention relates to engagement of focusing lenses with plastic shells for enclosing infrared light detectors.
2. Related Prior Art
Various automatic control apparatuses have been used in order to help people perform various tasks. Automatic control apparatuses often employ detectors which are able to detect infrared light emitted from objects within certain distances therefrom. As such detectors are often installed outdoors, they are exposed to the weather, therefore, they must be enclosed in shells for protection of their electric parts. Concave lenses are mounted in openings formed in the shells so that infrared light is allowed to penetrate the focusing lenses in order to reach the detectors.
In a first type of conventional detector, a rectangular opening is formed in a shell so as to form a lower horizontal rim, an upper horizontal rim and two vertical rims. A slot is formed in the lower horizontal rim of the shell. Accordingly, a focusing lens has a lower horizontal rim, an upper horizontal rim and two vertical rims. The lower horizontal rim of the focusing lens is received in the slot formed in the lower horizontal rim of the shell. The upper horizontal rim of the focusing lens is disposed against the upper horizontal rim of the shell. Glue is provided in the slot and between the upper horizontal rim of the focusing lens and the upper horizontal rim of the shell. Thus, the focusing lens is mounted on the shell. In accordance with a second type of prior art, the focusing lens is only glued on the shell. In the above-mentioned types of prior art, the engagement of the focusing lenses with the shells is not sufficiently firm as the focusing lenses are basically glued on the shells. If a gap occurs between a focusing lens and a shell, electric parts received in the shell will be exposed to the weather. Therefore, present invention is intended to solve the problem.